An analog-to-digital converter (ADC) is used to convert an analog signal into a digital signal for storing it in a digital memory or processing it with a computer. The digital signal in the memory may be converted into an analog signal by a digital-to-analog converter (DAC) for displaying the reproduced analog signal on a display device. One example of an electronic instrument having such functions is known as a digital storage oscilloscope. If a high-resolution ADC is used in a digital storage oscilloscope, the input analog signal is reproduced accurately and smoothly. However, high-resolution ADCs are expensive and complex in construction. On the other hand, if a low-resolution ADC is used in a digital storage oscilloscope, the displayed waveform is rough. This rough waveform is obtained because the output from the ADC includes an error of up to half of the least significant bit (LSB) of the ADC, and the value q corresponding to the LSB of a low-resolution ADC is larger than that of a high-resolution ADC.
Several techniques have been proposed to increase the ratio of signal-to-quantization noise of a digitized repetitive signal for enhancing apparent resolution so as to display the reproduced signal smoothly. One such technique is averaging, which accumulates values at corresponding points of the repetitive signal. Another technique is dithering, which offsets the corresponding points of the repetitive signal according to a predetermined algorithm. Dithering may also be used in conjunction with averaging. Averaging is not applicable to single-shot waveform acquisition and display.